The Multiple-Input Multiple-Output (MIMO) technology is a key technology of the third generation (3G) and the fourth generation (4G) mobile communication systems, which can increase the system capacity, improve the transmission performance, and be perfectly integrated with other technologies in the physical layer. However, if the correlation between the channels is relatively strong, the diversity gain and the multiplexing gain brought by multipath channels can be reduced greatly, thereby greatly reducing the performance of the MIMO system. Presently, a new MIMO precoding method is provided, which is a high efficient MIMO multiplexing method, a MIMO channel can be divided into a plurality of independent virtual channels through precoding processes on receiving/transmitting ends, thus the impact of the channel correlation is effectively eliminated, and therefore the precoding technology can ensure the stability of the MIMO system under different circumstances.
The Long Term Evolution (LTE) system is an important plan of the third generation partnership. The precoding technology in the LTE is realized by setting a codebook (a set of precoding matrices) in User Equipment (UE) and evolved Node Base (eNodeB), and the UE selects an optimum precoding matrix from the codebook based on a certain principle (for example, maximized throughout capacity, or the right singular matrix closest to the channel matrix), and feedbacks a Precoding Matrix Index (PMI) to the eNodeB, the eNodeB looks for the corresponding precoding matrix in the codebook according to the received PMI, and uses the precoding matrix to perform precoding transmission in the downlink transmission, in addition, Rank Instruction (RI) information is required to be fed back in the uplink channel, and the RI information indicates the maximum number of symbols that can be transmitted on a sub-carrier.
FIG. 1 shows a structure schematic view of a basic frame structure in the LTE system. As shown in FIG. 1, a frame structure is classified into four grades: radio frame, half frame, sub-frame, slot and symbol, wherein the length of a radio frame is 10 ms, and a radio frame comprises two half frames with the length of 5 ms each; a half frame comprises five sub-frames with the length of 1 ms each; a sub-frame comprises two slots with the length of 0.5 ms each.
When the LTE system uses a normal cyclic prefix, a slot comprises seven uplink/downlink symbols with the length of 66.7 us each, wherein the length of the Cyclic Prefix (CP) of the first symbol is 5.21 us, and the length of the cyclic prefixes of the other six symbols is 4.69 us each.
When the LTE system uses an extended cyclic prefix, a slot comprises six uplink/downlink symbols with the length of 66.7 us each, wherein the length of the cyclic prefix of each symbol is 16.67 us.
A Resource Element (RE) is a sub-carrier in an orthogonal frequency division multiplexing (OFDM) symbol, and a downlink Resource Bock (RB) comprises twelve continuous sub-carriers and seven continuous OFDM symbols (or six OFDM symbols when the CP is the longer ones), which is 180 kHz in the frequency domain, and is a time span of a normal slot in the time domain. FIG. 2 shows a structure schematic view of a resource block of the LTE system with 5 MHz bandwidth. As shown in FIG. 2, when performing resource distribution, the resource block is taken as the basic unit to be distributed.
When a target user feeds back the RI information, if the target user does not need to transmit data, the RI information is transmitted in a Physical Uplink Control Channel (PUCCH), if the target user needs to transmit data, the RI information is transmitted in the Physical Uplink Shared Channel (PUSCH).
The formats of the PUCCH are classified into 6 types, which are format 1, format 1a, format 1b, format 2, format 2a and format 2b, wherein format 1 is used for transmitting 1-bit Scheduling Request (SR) information representing that the SR exists or not; format 1a is used for transmitting ACK/NACK (acknowledgement/negative acknowledgement) information of 1-bit single codeword flow; format 1b is used for transmitting ACK/NACK information of 2-bit dual codeword flow, wherein each codeword corresponds to 1-bit ACK/NACK information; format 2 is used for transmitting Channel Quality Indicator (CQI)/PMI and the RI information; format 2a is used for transmitting the CQI/PMI and the RI information, the ACK/NACK information of the single code word flow, and is used in the case that the CP is a normal CP; format 2b is used for transmitting the CQI/PMI and the RI information, the ACK/NACK information of the dual codeword flow, and is used in the case that the CP is the normal CP. FIG. 3 shows a schematic view of the frequency domain position of the PUCCH in the LTE system. As shown in FIG. 3, each PUCCH channel occupies resources of two resource blocks; the length of the RI information is 1 bit or 2 bits, and when the RI information and the CQI/PMI information are transmitted in the same sub-frame, only the RI information is transmitted.
The channel structure of PUCCH format 2 is described hereinafter:
FIG. 4 shows a schematic view of the PUCCH channel for transmitting the RI information when the system uses the normal CP. As shown in FIG. 4, in the normal CP, a Constant Amplitude Zero Auto Correlation (CAZAC) sequence with a length of 12 is selected as the basic sequence, and the CAZAC sequence is repeated for 7 times, and each position of twelve frequency domains on each symbol of a resource block is mapped with one CAZAC sequence, wherein the sequences on the symbols of slot #0, #2, #3, #4 and #6 are used for transmitting the data on the PUCCH channel, and the sequences on the symbols of slot #1 and #5 are used for transmitting the Reference Signal (RS) on the PUCCH channel.
FIG. 5 shows a schematic view of the PUCCH channel for transmitting the RI information when the system uses the expanded CP. As shown in FIG. 5, in the expanded CP, the CAZAC sequence with a length of 12 is selected as the basic sequence, and the CAZAC sequence is repeated for 6 times, each position of twelve frequency domains on each symbol of a resource block is mapped with one CAZAC sequence, wherein the sequences on the symbols of slot #0, #1, #2, #4 and #5 are used for transmitting the data on the PUCCH channel, and the sequence on the symbol of slot No. 3 is used for transmitting the RS on the PUCCH channel.
The number of bits of the CQI/PMI and the RI information is 20 after coding. The coded bits will be processed by a Quadrature Phase Shift Keying (QPSK) modulation, and be modulated as ten QPSK modulation symbols. Each slot is mapped with five QPSK modulation symbols, and each modulation symbol corresponds to the data sequence of a PUCCH channel, the modulation symbol is multiplied with the target data sequence, is mapped onto a corresponding carrier, and then is sent out, wherein a Sounding Reference Signal (SRS) is transmitted in the last symbol of a sub-frame.
In the LTE system, the transmission of the uplink data uses the Single Carrier Frequency Division Multiple Access (SC-FDMA) method, which requires the uplink resources to be continuously mapped, and after the data to be transmitted on each symbol is modulated, a
Discrete Fourier Transform (DFT for short) process needs to be performed, and then to be mapped on the frequency domain position. If the PUCCH channel and the SRS are transmitted in the same symbol, an inter-code disturbance will be produced, thus the orthogonality of the codes between the PUCCH channels can not be ensured, thereby leading to a decline of the system performance.
In the LTE standard, when the uplink ACK/NACK information and the SRS are transmitted in the same symbol, the uplink ACK/NACK information will be transmitted using a short code structure; when the CQI/PMI information and the SRS are transmitted in the same symbol, the CQI/PMI information will be transmitted using the short code structure; when the SR information and the SRS are transmitted in the same symbol, the SR information is transmitted in the symbol, and the SRS is not transmitted; and for the method for transmitting the RI information and the sounding reference signal in the same sub-frame, the prior art does not provide a concrete proposal.